BACKGROUND There is controversial evidence regarding subacromial injections of nonsteroidal anti-inflammatory drugs and corticosteroid providing pain relief and restoration of function in shoulder impingement syndrome. We wanted to assess and compare the efficacy of subacromial ketorolac and steroids injections in treatment of patients with impingement syndrome. METHODS This study was a double-blind randomized controlled trial. The intervention groups included: A) Ketorolac; B) Triamcinolone; C) Betamethasone LA. The patients' pain was recorded based on Visual Analogue Scale system, and performance of patients was recorded based on Oxford Shoulder Score in 0, 2, 4, and 6 weeks. One-way ANOVA, chi-square test and repeated measurement were used to compare and analyse obtained results. RESULTS One hundred five patients were enrolled in the study. Three groups (each one containing 35 patients) were compatible in age and gender. Performance of patients was significantly improved in all three groups over time (p<0.001). The mean pain score of all three groups was significantly decreased over time in the three groups (p<0.001). No significant difference was found for pain scores between the groups at different follow-ups. CONCLUSIONS The results of present study showed that ketorolac, triamcinolone, and betamethasone are equally effective in improving and reducing patients' performance and pain, respectively, in treatment of impingement syndrome.